State to remove Lake Carmi aeration system after determining it made cyanobacteria blooms worse

State officials have decided to begin removing an aeration system in Lake Carmi and may soon move forward with an alum treatment after finding the system actually exacerbated conditions creating harmful cyanobacteria in the lake.

The aeration system was installed to try and mitigate cyanobacteria blooms, which is sometimes called blue-green algae. Officials found it had “unintended consequences” of mixing phosphorus-rich bottom water with the rest of the lake, according to minutes from an April 16 meeting of the state’s Lake Carmi Coordination Team. That led to higher levels of phosphorus in the Franklin County lake’s surface water and “stronger, more protracted cyanobacteria blooms.”

“We have seen high levels of bloom reports every year since the original system has been on now,” Peter Isles, an environmental scientist with the Vermont Department of Environmental Conservation, said in an interview. “Through various lines of evidence … it does seem to have gotten worse.”

Lake Carmi, a 1,375-acre body of water located in Franklin just a few miles south of the U.S.-Canada border, has been plagued by severe cyanobacteria blooms for years , with major beach closures routine throughout summer seasons. Lake Carmi State Park boasts the largest campground in Vermont, drawing tourists from Canada as well as throughout the state, and the blooms have been a drag on tourism and recreation.

“We had some awful, awful years,” said Rob Evans, the vice president of the Lake Carmi Campers Association. “We had algae blooms so thick that it looked like you could walk across our lake.”

The state has worked for decades to limit phosphorus runoff into the lake. An agreement with the federal Environmental Protection Agency in 2009 aimed to reduce phosphorus coming into the lake by 40%.

In 2018, the state declared Lake Carmi “a lake in crisis,” a designation that gave the Vermont Agency of Natural Resources authority to intervene. It opted to install the $1 million aeration system in 2019, in part because it was less invasive than other treatment options, Isles said.

The system worked by sending compressed air through a tube to a “manifold,” which shot the air into 40 different pipes spread out at the bottom of the lake. It was partly successful in reducing thermal stratification, a process that encourages the release of phosphorus at cooler bottom layers.

But the system repeatedly malfunctioned, making it difficult for state officials to conduct a comprehensive assessment of the system. Still, officials, observing an increase in blooms over three consecutive summer seasons, suspected that the system was not working effectively .

“That made the decision to discontinue it easier,” Isles said. “It’s not just that it wasn’t working so well. It’s that we really thought it was making it worse.”

The system will be removed in the fall, according to the Lake Carmi Coordination Team minutes. Officials said it’s unclear how much that will cost.

Evans said he doesn’t see the aeration system’s failure as a setback and pointed to the state’s continued investment into the lake.

“We’ve had several state agencies that were willing to invest a significant amount of money in what they hoped was going to be a solution, and unfortunately, it’s not,” he said. “I commend the state for not trying to continue to push it and wish that a system was going to work (when) the data showed us that the system is not working.”

‘Cautiously optimistic’

Now, the state and local community hope to move forward with a new treatment that would use aluminum sulfate to combat cyanobacteria in the water — a strategy that has been used in other Vermont lakes and one officials say could help combat the legacy nutrients that have built up over decades.

A feasibility study conducted by Barr Engineering, which began in October and is now being finalized, confirmed that blooms are being driven by nutrients at the bottom of the lake and concluded that aluminum treatment would significantly reduce phytoplankton blooms and improve lake clarity. Officials have pegged the cost of treatment at roughly $2.6 million.

Since aluminum naturally binds with phosphorus, the objective of that treatment would be to keep phosphorus locked into the lake’s sediment and thus unable to fuel cyanobacteria growth.

Lake Morey, in Fairlee, had a “very successful” alum treatment in 1986 and is in “better shape” since the treatment, according to meeting minutes from the Lake Carmi Coordination Team meeting.

Aluminum sulfate, at certain pH levels, can be toxic to certain organisms, but federal EPA and state guidelines ensure that treatments stay within acceptable thresholds, Isles said.

Brooks Sturtevant, the vice chair of the Franklin Selectboard, said he knows some residents who “are concerned about putting chemicals into a lake that is already dealing with chemical issues.” But, he continued, “in my conversations, from what I have heard, it’s more like, ‘Let’s try something that hopefully works.’ There seems to be some optimism.”

The state plans to review the draft feasibility study, according to Bethany Sargent, the deputy director of the state Department of Environmental Conservation’s watershed management division. If it determines that it’s a feasible option, the town of Franklin or the Lake Carmi Campers Association could then apply to the state for a permit to carry out the treatment.

Treatment could begin as early as next spring or by the fall of 2025, Sargent said.

Neil Kamman, the director of the Department of Environmental Conservation’s water investment division, said the state’s Clean Water Board approved $750,000 for Lake Carmi for fiscal year 2025 budget — which could help pay for the treatment.

The remaining balance, Kamman said during the April 16 Lake Carmi Coordination Team meeting, could be covered through several options. He recommended the town and community apply for a forgivable loan through the Clean Water State Revolving Loan Fund — dollars that would be available in spring of next year.

Other options included a direct request to the federal delegation for congressionally directed spending or for state capital appropriations.

For now, Evans said he and the community remain “cautiously optimistic” that they’re on a good path forward.

“I think anything that can help, people are willing to try,” Sturtevant said.

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